In high power radio applications, a very large and expensive filter is often used to separate transmit and receive signals. This is especially true when a system consists of a high power transmitter as well as a sensitive receiver where the transmit and receive bands are very near each other.
In a typical radio, there is a transmit chain and a receive chain. The transmit chain will have an associated gain, which will directly amplify the thermal noise. This thermal noise can fall in the receive band and must be filtered. In radio systems that have complex modulated waveforms, intermodulation noise from the power amplifier can fall into the receive band in addition to the amplified thermal noise of the transmit chain. In other cases where a more efficient class of amplifier is used in conjunction with pre-distortion, the pre-distorter can add noise as well. These noise sources place a requirement on the filter for the amount of rejection required in the receive band to block the transmitter from degrading the sensitivity of the receiver.
Another issue present in a typical radio system is that of the transmit carrier power getting into the receiver. This power is not in band and thus can be filtered out, but it must be filtered enough that none of the receiver chain saturates. This places an additional limitation on the filter.
Accordingly, there is a need for improved self-interference cancellation antenna methods and systems. Various aspects of the disclosure may solve one or more of these problems and/or disadvantages.